Radio position indicating system and apparatus



May l, 1951 J. E.v HAwKINs ET AI.

RADTo POSITION TNDICATING sYsTEIII AND APPARATUS 5 sheets-sheet 1 FiledJune 2l.' 1949 I I I I I I I I I I I I I I I QM QQNN NII.

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I I I I l I I I I l I I I I I I I l I l I l I I l III o a ES E Ss ISMQQMQ MSSS QQKQ Six Inl- QSSSSGW ul Y INVENToRs James f. Hawkins BYqeveffy W, KocplD-Z 5 Sheets-Sheet 2 www J. E. HAWKINS I'AL RADIOPOSITION INDICATING SYSTEM AND APPARATUS May 1, 1951 Filed JuneZl, 1949J. E. HAWKINS ETAL RADIO POSITION INDICATING SYSTEM AND APPARATUS May 1,1951 s sheets-smet :s

Filed June 2l, 1949 www www n May 1 1951 J. E. HAwKlNs raI-Au.A 2,551,2M

RADIO POSITION INDIOATINO SYSTEM AND APPARATUS Filed June 21, 1949 5sheets-sheet 4 JNVENTOM. James f. Haw/ 1115 f everlyh! @apfel May 1,1951 J. E. HAwK|N$ ETAL 2,551,211

- RADIO POSITION INDICATING SYSTEM AND APPARATUS Filed June`2`1, 1949 5sheets-sheet 5 46 leo VEN TORS. James i awkz'rzs BY f ever/y W MeppelvPatented May 1, 1951 arent ortica RADO POSITEON INDICATING SYSTEM ANDAPPARATUS Delaware Application June 21, 1949, Serial No. 100,382

The present invention relates to receiving and translating apparatus forradio position finding systems and more particularly to improvements inreceiving and translating apparatus including phase comparison andindicating means for use in radio position finding systems of thehyperbolic, continuous wave type employing phase comparison in pairs ofposition indication signals radiated from at least three spacedtransmitting points to provide indications from which the position of amobile receiving point relative to the known positions of thetransmitting points may be determined.

e In systems of the particular type referred to, the continuous wavesradiated from each pair of transmitters produce standing waves in space,the phase relationship of which changes as a ,function of changingposition between the two transmitting points. More specifically, thestanding Waves produced by each pair of transmitting units of the systemareV characterized by iso-phase lines which are hyperbolic in contourabout the transmitting points as foci. On a line bisecting the pair oftransmitters, these isophase lines are spaced apart a distance equal toonehalf the mean wavelength of the radiated waves and have divergingspacings at points on either side of this line. With this systemarrangement, the position of a receiving point relativezto a pair ofhyperbolic iso-phase lines may Y be determined by measuring the phaserelationship between continuous waves radiated from the pair oftransmitters. Since the point of location of the receiving point alongthe zone separating the two iso-phase lines is not indicated by such aphase measurement, it becomes necessary to employ at least three spacedtransmitters, different pairs of which function to provide a gridlikepattern of intersecting hyperbolic lines, in order to obtain absolutedetermination of the position of the receiving point.

lSystems of the character described are exceedingly accurate in so faras the position indications produced at the receiving point areconcerned. To obtain the desired indication accuracy, however, it isnecessary to maintain phase synchronization between the continuous wavesradiated by the spaced transmitters, or alternatively, so to arrange thesystem that phase shifts between the radiated waves are compensatedduring the phase comparing operation. Phase synchronization of the wavesradiated from the plurality of transmitters presents an exceedinglydifficult problem which has been the subject of considerable development15 Claims. (Cl. 343-105) work. All solutions which have been found forthis problem involve the use of relatively elaborate and somewhatdelicate instrumentation not well adapted for the continuity of servicerequired in position determining systems. To obviate this problem,systems of the continuous wave hyperbolic type have been proposed inwhich the phase shift problem is obviated by heterodyning the carrierwaves of each pair of transmitters at a fixed link transmitting point,and modulating the difference frequency component of the heterodynedwaves as a .reference signal upon the carrier output of the linktransmitter for radiation to the receiving point, where the differencefrequency component is detected and phase compared with a differencefrequency signal derived by directly heterodyning the transmittedcontinuous waves at the receiving point. In this manner, phase shiftsbetween the continuous waves radiated from the two transmitters arecompletely compensated so that the measured phase angle is trulyrepresentative of the location of the receiving point between a pair ofiso-phase lines.

While receiving and translating apparatus embodying the presentinvention is highly useful in systems of the type described and islikewise capable of more general application where phase comparison ofcontinuous wave signals is desired, such receiving and translatingapparatus is particularly applicable to radio position finding systemsof the type described and broadly claimed in copending applicationsSerial No. 778,796 led October 9, 1947, now Patent No. 2,513,317 issuedJuly 4, 1950, in the name of James E. Hawkins and Robert S. Finn, andSerial No. 42,648 led August 5, 1948, now Patent No. 2,513,318 issuedJuly 4, 1950, in the name of James E. Hawkins and Beverly W. Koeppel,which applications are assigned to the same assignee as the presentinvention and as to the latter of which this application is acontinuationin-part.

In the systems disclosed in the said copending applications the numberof frequency channels required is minimized by so arranging the systemthat two of the three transmitting units forming a complete system arealternatively employed to radiate the required position indicating andreference signals. More specifically, the two combination positionindicating and reference signal transmitters function to radiate pureunmodulated carrier wave energy when operating as position indicatingsignal transmitters and to radiate the same carriers modulated withreference signals when operating as reference signal transmitters andthe two receivers at t e receiving station alternately receive the twotypes of signals to produce equal frequency ignals for phase comparison.In order to minimize errors of position indications due to minorfrequency changes and amplitude variations in the signals to becompared, means are provided in the receiving equipment disclosed inapplication Serial No. 42,648 for maintaining amplitude equality of thesignals to be phase compared and for compensating for phase shifts`introduced into the phase comparing circuit by changes in the frequencyof the signals.

It is an object of the present invention to provide improved receivingand phase comparing apparatus which is uniquely adapted for use in aposition determining systemk of the character described.

It is a further object of the invention to proa vide an extremelyaccurate phase comparison and indicating apparatus.

It is another object of the invention to provide a null type phasecomparison system for continuously and accurately indicating therelative phase diiference between a pair of equal frequency signals.

It is still another object of the present 1nvention to provide improvedphase comparison systems capable of indication over more than a 360range and including means for readily effecting zero setting of thesystem.

According to a still further object of the invention, an improved phasecomparison system is provided which is relatively insensitive to changesin the relative amplitudes of the two input signals-and hassubstantially the same degree of sensitivity to phase changes betweenthe two input signals in all zones of a 360 indicating range.

The invention, both as to its organization and method of operation,together with further objects and advantages thereof, will best beunderstood by reference to the specification taken in connection withthe accompanying drawings, in which:

Figs. l, 2 and 3 when arranged vertically in order with the longdimension of each sheet disposed horizontally diagrammaticallyillustrate an improved radio position determining system includingreceiving and translating or phase comparing apparatus characterized bythe features of the present invention;

Fig. 4 is a front elevational View of a physical embodiment of one ofthe indicators shown diagrammatically in Fig. 3;

Fig. 5 is a side elevational view of the indicator shown in Fig. 4;

' Figs. 6 and 7 are sectional elevational views taken respectively alongthe lines 6 6 and I-'I of Fig. 5;

Figs. 8 and 9 are fragmentary detail elevational views on a somewhatenlarged scale respectively taken from the front and rear of a portionof the mechanism shown in Figs. 4 'to '7, inclusive; and

Fig. 10 isa sectional view on a somewhat enlarged scale takensubstantially along the line IIJ-I0 of Fig. 4.

Referring now to the drawings and more particularly to Figs. 1, 2 and 3,the present invention is illustrated as embodied in a system forproviding position information at a mobile receiving unit I3 which maybe carried by a vessel or vehicle operating within the radius .unit I Iof transmission of three spaced transmitting units Il?, I l, and i2.These units are preferably spaced apart approximately equal distancesand are so positioned that the line bisecting the points of location ofthe units Il) and I I is angularly related to the line bisecting thepoints of location of the units II and I2. As described more fullybelow, the transmitting units Il) and I2 are equipped continuously toradiate position indicating signals in the form of carrier waves ofdifferent frequencies, whereas the transmitting unit II is equippedalternately to radiate two additional position indicating signals in theform of carrier waves of still different frequencies. Specifcally, thetransmitter embodied in the unit I0 comprises a carrier wave generatoror oscillator I4 and a modulator and power amplier unit I5. Similarly,the transmitter embodied in the transmitting unit I2 comprises a carrierwave oscillator or generator I1 and a modulator and power amplifier unitI 8. The transmitting comprises two transmitters 26 and 2| forrespectively radiating position indicating carrier waves at twodifferent carrier frequencies, together with switching means foralternately rendering these two transmitters operative, In order toillustrate the action which occurs, arrow pointed solid lines have beenshown in Fig. 1 of the drawing to indicate the receiving points ofsignal acceptance and the sources of the accepted signals during eachperiod when the transmitter 26 is operating. and arrow pointed dashedlines have been shown to illustrate the receiving points of signalacceptance and the sources of accepted signals during each period whenthe transmitter 2i is operating. From a consideration of these lines andthe following explanation, it will be understood that the receivers 26and 2l (to be more fully described hereinafter) alternately function asreference signal detecting receivers and as heterodyning receivers fordeveloping the required heterodyne or difference frequency signals. Inthe arrangement illustrated, keying of the two transmitters 2B and 2lfor alternate operation is accomplished by alternately feeding anodecurrent to the electron discharge tubes of the respective transmittersfrom the positive terminal 25 of the anode current source, not shown,through a commutating ring 22 which is shaft connected by means of ashaft 24 to be driven at a constant speed by a synchronous motor andgear train unit 23. More specifically, the positive terminal 25 of theanode current source is connected to the conductive segment 22h of thecommutatingv ring 22, which segment spans slightly less than half thecircumference of the ring. The remainder of the ring is comprised of aninsulating segment 22a. At diametrically opposed points around thecircumference of the ring, brushes 22e .and 22d are provided whichengage the ring periphery. These b-rushes are respectively connected tothe positive bus conductors of the two transmitters 2l! and 2 I, suchthat anode current is alternately delivered to the electron dischargetubes of the two transmitters. Since the conductive segment 221) of thering 22 represents slightly less tha-n half the peripheral surface ofthe ring, itv will be understood that a short off-signal period isprovided between successive periods during which the transmitters 2i!and 2I are alternatively operated, thus preventing simultaneousradiation of waves by both transmitters. The periodicity with which thetwotransmitters 20 and 2I are alternately operated is, of course,dependent upon the speed of rotation of the commutating ring 22.Preferably, this ring is driven at a speed of one revolution per secondsuch that the transmitters 20 and 2I are each rendered operative atone-half second intervals.

As indicated above, the carrier frequencies at which the fourtransmitters of the three transmitting units I0, il and I2 operate areall different. Preferably, however, these carrier waves are so pairedthat the frequencies of each pair are Well within a single channelallocation of kilocycles as specified by the Federal CommunicationsCommission of the United States Government. To this end, the outputfrequency of the transmitter 26 and the output frequency of thetransmitter in the unit I2, forming the first transmitter pair, may be1601.875 and 1602.125 kilocycles respectively, such that the differencefrequency therebetween is 0.250 kilocycle, while the output frequenciesof the transmitter 2I and the transmitter of the unit I0, forming thesecond transmitter pair, may be 1699.700 and 17 00.300 kilocycles,respectively, such that the difference frequency therebetween is 0.600kilocycle. It will be noted that the channels in which the two pairs ofcarrier frequencies fall are separated in the frequency spectrum byapproximately 100 kilo-cycles, thus facilitating selective reception ofthese carrier pairs in the manner more fully explained below. The powerof the four transmitters is such that the entire area in which positioninformation may be desired abroad the vehicle or vessel carrying thereceiving unit I3 is blanketed with waves radiated from each of the fourtransmitters and that these waves have a field strength at all pointswithin this area suiiicient to permit reliable reception withoutrequiring undue sensitivity of the receiving equipment.

In order to obviate the above mentioned diiculties attendant with phasesynchronization of the position indication carrier waves radiated by thefour transmitters, while at the same time eliminating the necessity forutilizing additional frequency channels, means are provided in thetransmitting units I0 and I2 for alternately modulating the wavesradiated by the transmitters of the units I0 and l2 with referencesignals repsentative of the diierence frequencies between the carrierwave pairs. These reference signals may be received at any receivingpoint, such, for example, as at the mobile receiving unit I3, locatedwithin the radius of transmission of the four transmitters. pose asprovided at the transmitting unit I0 comprises a xed tuned amplitudemodulation receiver I6, center tuned to a frequency of 1602 kilocyclesand sharply selective to the 1601.875 and 1502.125 kilocycle carrierwaves respectively radiated by the transmitter and the transmitter ofthe unit I2. The selectivity of this receiver is obviously such that thecarrier waves radiated by the transmitter 2I and the transmitter of theunit I6 are rejected in the radio frequency section thereof. The beatfrequency of 0.250 kilocycle between the two carriers accepted by theradio frequency section of the receiver IS is reproduced in the audiofrequency section of this receiver and delivered to the modulator I5,for amplitude modulation upon the carrier output of the transmitterembodied in the unit Iii, through a narrow band pass filter 8, which iscenter tuned to a frequency of 0.250 kilocycle. Similarly, thetransmitting unit .I2 is equipped with a iixed tuned amplitudemodulation receiver i9 which is tuned to a carrier fre- The equipmentfor this purquency of 1700 kilocycles and is sharply selective to the1699.700 and 1700.300 kilocycle waves respectively radiated by thetransmitter 2I and the transmitter of the unit l0. Here again, theselectivity of the receiver I9 is obviously such that the carrier wavesradiated by the transmitter 20` and the transmitter of the unit I2 arerejected in the radio frequency section of the receiver. The'beatfrequency of 0.600 kilocycle between the -two carrier Waves accepted bythe receiver I9 is reproduced in the audio frequency section thereof andmodulated upon the carrier Wave output of the transmitter embodied inthe transmitting unit I2 through a narrow band pass filter 9 which iscenter tuned to a frequency of 0.600 kilocycle. g

Referring now particularly to the receiving and translating equipmentmaking up the mobile receiving unit I3 and the phase comparisonapparatus associated therewith, it is pointed out that this equipmentcomprises a pair of iixed tuned amplitude modulation receivers 26 and21, the output circuits of which are connected to the phasediscriminators 28 (Fig. 2) and 29 (Fig. 3) and the indicators 30 and 3|(Fig. 3) through suitable amplifier and automatic gain or volume controlstages 32 and 33 and through suitable narrow band pass iilters 34, 35,36 and 31, the band pass iilters 34 and 35 being center tuned to afrequency of 0.600 kilocycle and the filters 3,6 and 3l being centertuned to a frequency of 0.250 kilocycle. More specifically, the receiver26 is fixed tuned to a carrier frequency of 1700 kilocycles and isdesigned to accept the carrier wave radiated by the transmitter 2l andthe carrier wave radiated by the transmitter of the unit I0 both whenmodulated and unmodulated. Similarly, the receiver 2l is xed' tuned to acarrier frequency of 1602 kilocycles and is designed to accept thecarrier wave radiated by the transmitter 20 and the carrier waveradiated bythe transmitter of the unit I2 both when modulated andunmodulated.

The automatic gain control or AVC circuits associated with the amplifierstages 32 and 33 are of the variable impedance type known in the art andcapable of functioning without introducing amplitude distortion orvariable phase shift in the reference signals and the heterodyne ordifference frequency signals developed at the output terminals of thereceivers. Preferably the amplifier and AVC stages are of the typedisclosed in a copending application of James E. Hawkins and Jesse R.Cornett, Serial No. 673,744 iled June l, 1946, for Seismic SignalAmplifier and assigned to the same assignee as the present invention andeach of these stages corresponds to the automatic gain control andamplifier stage identified by the reference number 13 in the saidHawkins and Cornett application.

The lters 35 andy 36, 34 and 37, which may be of any standard commercialconstruction, perform the function of selecting the heterodyne ordifference frequency signals alternately developed at the outputtermina-ls of the receivers 26 and 21, respectively, and amplied in thestages 32 and 33, and delivering these signals to the phasediscriminators and indicators as hereinafter described.

In considering the operation of the abovedescribed position determiningsystem, it will be understood that when the motor and gear train unit 23is operating to drive the commutating ring 22, anode current isalternately delivered to the electron discharge tubes of thetransmitters 20 and 2|, such that these transmitters are aachen 7alternately rendered operative to radiate carrier waves at frequenciesof 1601.875 and 1699.700 kilocycles, respectively. The transmitters ofthe units I and I2, on the other hand, -operate continuously.Accordingly, during each interval wehen Vthe transmitter 20 is inoperation, the carrier yWaves of 1601.875 and 1502.125 kilocyclesrespectively radiated by the transmitter 2li and the transmitter of theunit I2 are picked up and lieterodyned in the radio frequency sectionsof the'receivers I0 and 27. In the receiver i5, the difference frequencysignal of 0.250 kilocycles is reproduccdin the audio section of thereceiver, passed by the filter 8 and modulated upon the carrier waveoutput of the transmitter in the unit Iii-for radiation as a referencesignal. if desired an ampliiier automatic gain control stage similar tothe stages 32 and may be interposed in the output circuit of thereceiver I in order to Amaintain constant modulation. This modulatedca'rrier wave is received by the receiver 20 of the mobile receivingunit i3 and the 0.250 isilocycle modulation component is reproduced atthefoutput terminals of this receiver. During the period indicated, thetransmitter 2I is not in operation and hence no heterodyne or beat fre--quency signal is developed by the receiver 2G. The. 0.250 kiiocyclereference signal as thus reproduced by the receiver 25 is amplified tothe proper level in the amplifier and AVC stage 32 and appliedby way ofthe conductors 30 to the input terminals of the band pass filters o5 and"ihe0.600 kilocycle filter 35 rejects the applied signal2 and thusprevents the same from being applied to the phase discriminatoi` 28, butthe nite-r- 35 passes the signal to the input terminal of the phaseindicator 3 l.

The 0.250 kilocycle beat frequency or heterodync signal resulting fromheterodynng of the carriers radiatedby the transmitter 20 and thetransmitter of the unit I2 in the radio frequency section of thereceiver2l' is reproduced across the output terminais of this receiverand after amfplication to the propel' level in the ampliiier and AVCstage 33 is applied through the conductors 4I to the input terminals ofthe band pass filters it and 3 1 in parallel, The 0.500 kilocycle lter34 prevents the 0.250 liilocycle signal from being applied to theindicator 30 but the lter 37 passes the 0.250 kilocyclc signal developedacross the output terminals of the receiver 2l' and applies the same tothe upper input terminal 02 of the phase discriminator 2S. Thus twosignal voltages of identical frequency are applied to the inputterminals i2 and 10 of the associated phase discriminator and phaseindicator 29 and SI, which function hereinafter explained to measure thephase angle therebetween. The phase angle indication thus obtained isaccurately representative of the position. of the receiving unit i3between two izo-- phase lines of the standing waves produced in space asa result of the carrier wave radiation by the transmitter 20 and thetransmitter of the unit I2.

At the end of the described transmitting intei-val, the commutating ring22 functions to interrupt the circuit for delivering anode current tothe tubes of the transmitter 20, with the result that carrier waveradiation from this transmitter is terminated. When radiation of thiswave stops, the carrier heterodyning action of the two receivers I5 and2? is likewise terminated to interrupt the reference signal radiation bythe transmitter of the unit I0 and to interrupt the heterodyne ordifference frequency signal being developed across the output terminalsof the receiver 2l. Thus the phase discriminator 2 9 and the indicatorSIy are rendered ineffective further to change the setting of theindicating element of the indicator SI.

A short time interval after operationrof the transmitter 20 is stopped,the commutating ring 22 functions to deliver anode current to the tubesof `the transmitter 2! and thus initiate operation of this transmitter.With the transmitter 2l in operation, a 1699.700 kilocycle positionindicating carrier wave is radiated thereby which is accepted by thereceivers I9 and 26. More specifically, the receiver I0 functions toheterodyne the carrier Wave radiated by the transmitter 2l with thecarrier wave radiated by the transmitter of the unit iii and toreproduce the heterodyne or diiference frequency signal of 0.600kilocycle in the audio frequency section thereof. r1"'his differencefrequency or reference signal is passed by the lter 9, modulated uponthe output carrier wave of the generator il' in the modulator and poweramplifier unit I8 and radiated as a modulation component upon thecarrier wave transmitted by the transmitter of the unit i2 to thereceiver 2l. As previously mentioned in connection with the receiver I6of unit i0, a suitable amplifier and automatic gain control stage maybeinterposed in the output circuit of the receiver i9 in order tomaintain constant modulation. The receiver 2l accepts the modulatedcarrier waveand reproduces the modulation component thereof in the usualmanner. The reference signal thus developed across the output terminalsof the receiver 2l' is amplified to the proper level in the amplifierand AVC stage 33 and applied through the conductors ci to the inputterminals of the band pass filters 34 and 3l in parallel. The filter Elfunctions to reject the applied reference signal voltage and thusprevents the same from being impressed upon terminal i2 of the phasediscriminator 29, but the filter 34 passes the 0.600 kilocycle referencesignal to the upper input terminal 4S of the indicator 30. It will beunderstood that the receiver 2l is incapable of accepting the carrierwave radiated by the transmitter of the unit I0. Hence this receiver isprevented from heterodying the carrier wave radiated by the transmitterof the unit I0 with the carrier wave radiated by the transmitter of theunit I2.

The 1699.700 and 1700.300 kilocycle lwaves respectively radiated by thetransmitter 2I and the transmitter of the unit I0 are both accepted bythe receiver 20 and heterodyned in the radio frequency section thereofto produce a heterodyne or difference frequency signal which is producedacross the output terminals of the receiver and after amplification tothe proper level in the amplifier and AVC stage Si. is applied throughthe conductors 39 to the input terminals of the filters and 36 inparallel. The filter 36 rejects the signal voltage, thus preventing itsapplication to the terminal i0 of the indicator 3I, but the 0.600kilocycle reference signal is passed by the filter 35 and applied to theinput terminal :lai of the phase discriminator 2t. Thus reference andheterodyne o r difference frequency signals of identical frequencies arerespectively applied to the input terminals 44 and 3 of the associatedYphase discriminator and phase indicator 28 and 30, which function ashereinafter explained to measure the phase relationship between the twoapplied signal voltages and thus provide an indication accuratelyrepresentative of the position of the receiving unit I3 between twoiso-phase lines of the standing waves produced in space by the radiationof position indicating carrier waves from the transmitter 2| and thetransmitter at the unit I0.

At the end of the described transmitting interval, the commutating ring22 functions to interrupt anode current iiow to the tubes of thetransmitter 2| and thus arrest operation or this transmitter. Whencarrier wave radiation by the transmitter 2| is thus terminated, thewave heterodying action effected in the receivers IB and 26 is instantlystopped to terminate the radiation of the 0.600 kilocycle referencesignal by the transmitter of the unit I2 and to terminate reproductionof the diierence or heterodyne signal at the output terminals of thereceiver 20. Thus the application of signa-l voltages to the inputterminals of the phase discriminater and indicator 28 and 30 isinterrupted, with the result that no further change in the setting ofthe indicating element of the indicator 30 can be produced. A short timeinterval after operation of the transmitter 2| is arrested, thecommutating ring 22 functions to recomplete the circuit for deliveringanode current to the tubes of the transmitter 20 and thus reinitiateoperation of this transmitter with the results described above.

From the foregoing explanation, it will be understood that thetransmitters 20 and 2| in their alternate operation to radiate positionindicating carrier waves, cooperate with the receivers I6 and I9 of thetransmitting units i0 and I2 alternately to render the transmitters ofthese units operative to radiate position indicating signals andreference signals. More in particular, the position indicating carrierwaves alternately radiated by the transmitters and 2i alternately causethe position indicating carrier waves respectively radiated by thetransmitters of the units I and I2 to be modulated with referencesignals during periods when these transmitters are respectively inactiveas position indicating signal radiators. Specifically, the receiver 26functions as a heterodyne receiver in respect to the position indicatingcarrier waves radiated by the transmitter 2| and the transmitter of theunit I, and functions as a reference signal reproducing receiver inreceiving the reference signal modulated carrier radiated by thetransmitter of the unit I0. The receiver 21 on the other hand, functionsas a heteredyne receiver in respect to the position indicating carrierwaves radiated by the transmitter 23 and the transmitter 'of the unit i2and as a reference signal detecting receiver in receiving the referencesignal modulated carrier wave radiated by the transmitter of the unitI2.

As will be evident from the above explanation, the associated phasediscriminator and indicator 29 and 3| function as hereinafter describedto produce a phase angle indication which is representative of theposition of the receiving unit I3 between two iso-phase lines of thestanding waves produced in space as a result of carrier wave radiation bythe transmitter and the transmitter of the unit l2. With the describedarrangement, wherein carrier wave frequencies of 1601.875 and 1602.125kilocycles are employed, the wavelength spacing between the isophaselines along a line bisecting the units II and i2 is determined by themean frequency of 1602 kilocycles between the two radiated carrierwaves. At this particular mean frequncy, isophase lines representativeof the same phase relationship between the standing waves produced bythe transmitter 20 and the transmitter of the unit I2 along the linejoining the unit 20 and the unit I2 are spaced apart a distance of about307 feet. Hence the indication provided by the indicator 3| identifiesthe position of the receiving unit I3 within a zone not less than 307feet in width, i. e., a Zone having a minimum width equal to one halfthe wavelength of a wave having a frequency equal to the mean frequencyof the position indicating carrier waves radiated by the transmitter 20and the transmitter of the unit I2.

As previously indicated, the indication provided by the indicator 3|,standing alone, is ambiguous for the reason that this indication doesnot identify the point of location of the receiving unit I3 along thezone separating the two adjacent iso-phase lines of the lines of thestanding Waves produced in space by the transmitter 2U and thetransmitter of the unit i2. Identification of this point is obtainedthrough the respons-e of the receiving unit to the position indicatingsignals radiated by the transmitter 2| and the transmitter of the unitI0. Thus, the phase discriminator and indicator 28 and 30 provide anindication of the position of the receiving point, namely, the unit I3,between two iso-phase lines of the standing waves produced in space bythe radiation of position indicating carrier waves from the transmitter2| and the transmitter of the unit I0. Here again, the wavelengthspacing of iso-phase lines along a line bisecting the two units I0 andII is determined by the mean frequency of 1700 kilocycles between thefrequencies of the waves radiated by the transmitter 2| and thetransmitter of the unit I0. At this particular mean frequency, isophaselines representative of the same phase relationship between the standingwaves produced by the two identied transmitters have a minimum spacingof approximately 289 feet, such that the indication provided by theindicator 30 identies the position of the receiving unit I3 vthesedistances known and the positions of the transmitting units II) and I2known, the position of the receiving point may obviously be easilydetermined.

Since the phase discriminators 20 and 29 are identical in constructionand operation, except for the frequencies to which they respond, andsince the same is true of the phase indicators 30 and 3l, only the phasediscriminator 23 and the phase indicator 3D have been illustrated indetail. The phase discriminator 28 which, as

indicated in Fig. 2, includes a motor drive network to be hereinafterdescribed, and the indicator 39 which includes a direct current motor 45for driving an indicating element or pointer 45 and the rotor of avariable phaser or control transformer 41, function together to providea follow-up type phase diierence measuring and indicating system, theoperation of which will be described, during an interval in which a0.600 kilocycle position indicating heterodyne signal is being appliedfrom the receiver 26 to the terminal lid of the phase discriminator 20and a 0.600

kilocycle reference signal is being applied from il the receiver 271 tothe terminal. 43 of the indicator 3D.

The. motor 45, which is preferably ofthe. type havinga permanent magneteld,. has. one.. terminal of its armature winding. connected to ground,as shown, and its other terminal is.connected by a conductor 48A to aninput terminal- 49 of the indicator 30, to which terminal is ap.- plieda direct current voltage derived. from the phase discrimina-tor 28,through the motor drive network thereof. As shownin Fig. 3, the directcurrent motor 45. is connected tothe indicator'. member or pointer 45.through reductiongearing comprising a worm 59 and a worm gear 5Icarriedby the shaft 52: on. which. thepointer 46 is mounted. The-pointer46 is. movable through more than 360 degrees withrespect to. asuitablycalibrated scalella- (Fig. 4) anda suitable revolution counter 53-is`connected .to the shaft'. 52 through bevel gears 54.

Themotor is likewise. connected.. through the worm and the worrngear 5.!andthrough..

a suitable. couplingmechanism. 55.. which willbe.

more fully described hereinafter.. to a shaft@ ony which is carried therotor. 51 (Eig. 10) ofi a variable. phaser or control transformer. 41.control transformer,y as shown in. Eig. 3,.is pro vided with a. rotorwinding. 58 and ay pair. otv

stator windings 59. and S0.. The stator windings '5S-and. 60 arearranged.mechanically-90. degrees` apart and are-connected tothe input.terminal. 43-soy as to be, electrically 90 degrees apart, the.

connection .to the winding 59. including a. re-

sistor 6! and a-condenser E2 for. providingthe.

desired phaseshift. With. the control. trans.i former 41- thusconnected, it. will be. apparent that. when the stator. windings areenergized.- with the 0.600 kilocycle reference signalsuppliedto theinput terminal 43-through the` band-pass. filter. 34, a voltageV willbe-induced. inthe rotor winding 58, which will be of. constant.amplitude but which will have a phaseV relation dependent upontherelative. position of theV rotor winding. 58 with. respect to the statorwindings 59 and.

Thus rotation of the-rotor winding 58y will pro-- duce -a variable phaseVoltage and, as shown,.

the rotor winding is connected by means of aY conductor 63 to an outputterminal (54V of the phase indicator 3u, which outputV terminal. isconnected by a conductor. 65 to an input terminal 66 of the-phasediscriininator 28..

Thus it will be seen that the inputv terminals 44'and 660i. the phasediscriminator -are supplied with 0.600. kilocycle signalshaving aphasediierence which is a function not only. of. the

position of the mobile. receivingV unit I3 but also of. the. position ofthe. rotor winding 58- of the variable phaser, and: therefore thepositioni of the indicating element or pointer 46.. As will be morefully explained. hereinafter, the phasediscriminatorand the motor'drivenetwork function to'produce a direct current voltage, the

tov the position indicating signal applied to theY input terminal 44 ofthe phase discriminator 28 such that the driving voltage applied tothemotor 45 will become zero. Consequently, the

The.

tiometers Si' and 68 to the upper and lowerconv trol grids @9 and 'lilof a. multi-section triode connected amplier tube 1i. The uppersec. ation. of the amplifier tube includes. a cathode .12-

and an anode or plate '13-v which, as showni are..

connected in an output. circuit which includesa pair of series connectedprimary windings'E-ll` .and-

Likewise the. lower section of theamplifer tube. 1|- includes a cathode'il and an. anode or plate. 'i8 which- 75 ci a suitable transformer 16.

are connected in a similar output-circuit which includesa pair of seriesconnected primary wind= ings 1.9 and-8) of a transformer 8|. The trans=former 15 includes. a pair. ofy center tappedsecH1 ondary windings 32and 83 respectively associi ated with the primary windings. T4-and15f,while. the tarnsformer 8l includes a-pair of secondarywindings 84 and 85respectively associated with the primary windings 79 and 80 and. adaptedto produce secondary voltages approximately equal. iny magnitude to thevoltages. produced.-. across half of each of the secondary windings.

82 and B3.

As shown, the outer terminalsof the. sf'ecomlar-yY winding. 82 arerespectively connected. to the upper and lower pla-tes 36 and 81 of a..double` diode. 88 and the center tap 89. of the. secondaryy winding S2is connected through a. conductor 99 to one terminal of the secondarywinding84`,y the opposite terminal of which is connected.

through a conductor 9| to a pair, of cathode resistors 92 and 93 whichare respectively con.-

nected asshown to the upper and lower cathodes. 94 and 95. of the doublediode 88..

smoothingcondensers 96 and 91 are respectivelyconnected across thecathode resistors-92. and-.93

Suitable for purposes well understood in the art..

Similarly, the outer terminals, of theA sec' ondary winding 93.arerespectively connected to the upper and lower plates 9i! and 99- of.a second double diode E99 and the center tap. lll.

ing 85, the other terminal ofwhich is. connectedv through a conductor m3to two cathode resistors H04 and $95, which are. respectively shunted bysmoothing condensers i96- and Illl and are respectively connected tothecathodes |08 and |09 ci thedouble diode l di?. As shown,. thecathodes and. 98, which. are. respectively connected inA circuit withthe lower half'of the secondary' windings?. and the upper half of thesecondary winding areconnected to ground' at H0, andthe .cathodes 4- and99, which are respectively connected in circuit with the upper half ofthe secondary winding S2 and the lower half of the secondary winding 33are connected to suitable output terminals Hi and H2. With the doublediode rectiers 83 and lil!) connected as shown', direct current outputvoltages are obtained at the terminals ill and H2 of equal magnitude andopposite polarity with respect to ground. These voltages areproportional in amplitude'to the phase diiierence between thetwosignals'applied at the terminals 44 and 6'6 and of polarities dependentupon the sense of the phase difference between the same two signals. Inother words, if one of the signals applied to the terminals 44 and B6changes from leading to lagging phase relationship with respect to theother signal, the direct current voltages at the output terminals and H2will reverse in polarity.

More specifically, analysis of the connections of the transformers T16and 8|, the double diode rectiers 88 and |60, and the cathode resistors92, 93, |54 and |95 with respect to the ground connection I I and theoutput terminals and II2, will show that when the signals applied at theterminals 44 and 6B are in phase with each other a maximum directcurrent output voltage of predetermined polarity will be developed atthe terminal I I, and when the input signals are 180 out of phase amaximum direct current voltage of opposite polarity wil be developed atthe terminal the direct current voltage passing through zero andreversing polarity when the input signals are 90 out of phase. The sameeffeet is produced at the terminal ||2 except that the voltages at theterminals iiI and ||2 are at all times of opposite polarity with respectto ground.

Connected to the output terminals II I and IIZ is an anti-hunt networkcomprising a pair of resistors ||3 and H4 which are connected to groundat ||5 and which are connected to the terminals and ||2 respectivelythrough condensers i I5 and the condensers being respectively shunted byresistors ||8 and H9. The anti-hunt network functions by reason of therelative magnitudes of the condensers ||6 and and the resistors ||3 and||4 to introduce into the signal voltages appearing at the termi.- nalsand ||2 a voltage component which is proportional to the rate of changeof the signal voltages, thus producing an anticipating eect, wherebyupon a sudden change in the applied signal voltages, the voltages at theoutput terminais and |2| of the anti-hunt network may fall to zero oreven reverse in polarity a predetermined interval ahead of the appliedsignal voltage. This arrangement prevents hunting of the D. C. rnotor 45which, as previously indicated, is energized by a direct current voltagederived from the signal voltages produced at the output terminals liland ||2 of the phase discriminator circuit. For a description of thetheoretical operation of anti-hunt networks of this type, reference maybe had to pages 15 and 28 of the Radio-Electronic-Engineering edition ofRadio News for August 1948.

The output terminals and |2| of the antihunt network are connected asshown to the upper and lower contacts |22 and |23 of a synchronousvibrator |24 having a pair of reeds |25 |25 adapted to be driven by anoperating magnet I2?, the primary winding of which is connected in anenergizing circuit comprising a battery |28, a choke coil |29, a contact|39, and the vibrator reed |26, the battery and the reed being connectedto ground at |32 and |3| respectively. A suitable condenser |33 isconnected across the operating magnet l2? and the make and break gapbetween the contact i3d and the reed for purposes well understood in theart.

The reed |25 of the vibrator |24, which is arranged alternately toengage the contacts |22 and |23 is connected by way of a conductor |34and a series coupling condenser |35 to the input electrode or controlgrid |36 of an ampliner tube I3? which is of the well known pentode typehaving a cathode |38, a screen grid |39, a suppressor grid |46 and aplate or anode |4I. It will thus be apparent that as the reed |25 of thevibrator |24 alternately engages the vibrator contacts |22 and |23, asignal will be applied to the control grid |36 of the amplifier tube|3`| which will be substantially a square wave signal whose frequencycorresponds to the frequency of the vibrator, whose amplitudecorresponds to the amplitude of the signals at the output terminals |26and I2| of the anti-hunt network, and whose phase depends upon therelative polarities of the same two signals. Thus, the phase of thesquare wave signal applied to the amplifier tube |37 depends upon thesense of the phase displacement between the signals applied to the inputterminals 44 and 65 of the discriminator.

rihe output of the amplifier tube |3`| is applied as shown to aconventional phase inverter |42 which is in turn connected to supply a,pair of power amplifier tubes |43 and |44 connected for push-pulloperation and having their respective anodes connected to the oppositeends of a center tapped primary winding |44a of a coupling transformer|45, the secondary Winding |46 of which is connected for full waverectification* to the rectier contacts |4I and |48 of the synchronousvibrator |24 through conductors |49 and' |56. The center tap |5| of thesecondary winding |46 is connected by way of a conductor |52, a radiofrequency choke |53, a conductor |54, a center contact |55 of a multipleposition switch |56, the purpose of which will be explained hereinafter,and the movable contact |51 of the switch |56 and a conductor |58 to theinput terminal 49 of the indicator 30. Since the vibrator reed |26operates in synchronism with the vibrator reed |25, which latter reedproduces the square wave voltage applied to the amplifier tubeI3`|,'full wave rectification of the amplified signal developed acrossthe winding |46 is obtained. During alternate half cycles of thisvoltage, the energizing circuit for the motor 45 may be traced from theground connection |3I, the reed |26, the vibrator contact |48, forexample, the conductor |50, and the upper half of the secondary winding|45 to the input terminal 49 and by way of the previously describedcircuit and the conductor 48 and the motor winding back to ground at theconnection |59. During intervening half cycles of the signal voltagedeveloped across the winding |56, the motor energizing circuit includesthe reed |25, the vibrator Contact |47, the conductor |49, the lowerhalf of the winding |46, the conductor |52, the choke coil |53, thecontact I 55 and switch blade |51, and the conductors |53 and 48. Whilethe vibrator |24 may be driven at any desired frequency, it ispreferably operated at a frequency far removed from the frequency of theinput signal voltages and may, for example, be driven at frequencies inthe neighborhood of 60 to 9G cycles f per Second.

As will be apparent from the foregoing description of the phasediscriminator and motor drive network, the motor 45 and the indicatormember or pointer 46 of the indicator 30 will remain at rest wheneverthe phase relationship between the two signals applied to the inputterminals 44 and 66 of the phase discriminator 28 is such that zerovoltage is developed by the phase discriminator and the motor drivenetwork. This condition prevails only when the signalvoltagesrespectively applied to the discriminator network input terminals 44 and66 are displaced-in phase byninety degrees. However, wheni the phase'of.

the position indicating heterodyne signal applied tothe input terminal44shifts dueto. movement of the. mobile receiving unit |3the; phasediscriminator and motor drive network develop a direct current voltageof the proper polarity to cause themotor 45 to rotate in a direction toadjust the rotor ofthe control transformer 41 and .thereby vary thephase ofv the signal voltage applied to the input terminal 65 so asYagain to establish aninety degree phase relationship between the twoinput signals, thereby to reduce to Zero the output voltage of thenetwork 28, whereupon the motor 45 and the pointer 46 vagain come torestin a position accurately indicating the position of the mobile receivingunit I3 relative to the transmittingi unit IB and the. transmitter 2|.

At the start of a` positiorrdetermining operation, it is necessary toinitiallyset' the revolution counter53. of. themulti-position switch.|55. which, in addition to the fixed contact |55Y and. the movablecontact |51, includes spaced stationary contacts |64l and |65 adapted tobe engaged bythe movable contact |51 and connected to direct currentsources of opposite polarity, such, for example, as the batteries lfand.|61., whereby thek motor maybe selectively energized through the movablecontact |51 for operation in'either direction tol set the revolutioncounter 53` in any desired initial position corresponding to the lane.position of the mobile receiving unit I3 at the start of a surveyoperation. At the` start ofa survey operation it is also necessaryto setthe pointer 45 of the indicator 3|) in the position corresponding'to theknown starting point `of the mobile receiving unit I3 and this maybe`accomplished by means of a manually operable control knobr |55carried on a rotatable shaft |6| which is effective through a pinion |52and arack. gear |63 to rotate the stator of the control transformer 41,thereby to change the angular position ofthe stator windings 59 and'rel'ativeto the rotor winding 58. This has the effectof'changing thephase relationship between the signal input voltages impressed upon thediscriminator network input terminals 44 and 66 and hence ofproducing'operation of the motor 45"to drivethepointer 46 and rotor 51in a manner clearly apparent from the above explanation.

In order to obtain the desired degree of accuracy inthe positionindications provided by the indicator 35, it is imperative that each onedegree of rotation of the pointer 45 must, through rotation of the rotorwinding 53 of the control transformer 41, produce a one degree phaseshiftA in the output voltage of therotor winding. The previouslyreferred to coupling unit 55 is connected between the motor 45 and therotor of the control transformer in order to accomplish this end in themanner' morey fully explained'` below.

As shown in Figs. 4 to 10, inclusiva. in which thepreviously identiedparts of the indicator 3|! are indicated by the same-referencenumerals,and as shown diagrammatically in Fig. 3, the worm gear i, which isdriven through the worm 55 by the motor 45, is provided' with a slotv oraperture |58 for receiving a pin |59 carried bya driving member |19forming a part-ofthe cou'- pling unit 55. may be in the form of a diskor a segment of. a disk, is mounted for free rotation on az stub shaft|1| (Fig. 10), to which is secured a collar A|12 having an extending arm|13; A resilient driv- This'may be accomplished by means i The drivingmemberl |13, which" vingx'connectionbetween;the'driving member |18 andthe collar |12 is. provided by means of. a

spring |14 which, as shown best in Fig. 9, has. oneend thereof connectedto the. member |10 andv The` 'l engage a continuous substantiallycircular, or socalled garter, spring |19. The spring |19, as shown bestin Figs. '1 and l0, is supported throughout its periphery on a pluralityof supporting lingers |89 carried onradially adjustable posts |5i, whichthreadedly engage-a circumferentialiy extending supporting ange |82.

When the driving member or disk |15 is rotated by the worm gear 5|,rotation of the rotor 51 will be eifectedseitherthrough the tendency-ofY the rotation to tighten. the spring |14 or through relaxation of thetension on the spring |14. At

. the same time, however, the lever |15 and the roller |18 will be movedand in order to effect unequal increments ofmovement of the rotor 51relative to incremental movement of the motor and the gear 5|, theperipheral configuration of. the garter spring |19 may be varied throughadjustment of the supporting posts |8| so that the roller |18 and thelink |15 will offer increased or decreasedresistance to movement, asdesired,

thereby causing the tightening or relaxation of the driving spring |14.By proper adjustment of the garter spring |19, the rotor 51 of thecontrol transformer 41 may be caused to move a distance greater or. lessthan the movement of the pointer 45, as may be required to insure a onedegree phase shift in the output of the rotorv winding 58 for each onedegree of movement of the pointer 46. Y

Preferably and in order to assist in the initial calibration of thecoupling unit 55, the annular supportingv member |82, which carries theadjustable posts |8|, is provided with suitable indicia |83 forcooperation with a pointer |84 carried on the stub shaft |1| of thecoupling member |12, and additional indicia |85 carried by the drivingmember |16 are provided for efecting adjustment at one degree intervals.

As previously indicated the phase discriminator 29 and the indicator 3in which previously identied correspondingconnections and componentsare. indicated by the same reference numerals, areidentical with thecorresponding units 23 and 30 except that they are energized, duringalternate intervals in which the transmitter 2S is operating, by the0.250 kilocycle position indicating heterodyne signal from the receiver21 and by the 0.250 kilocycle reference signal from the receiver 26 soas to produce a continuous indication of the position of the mobilereceiving unit relative to thev transmitting units and |2. Consequentlythe two indicators 35 and 3| are effective to produce a continuous,accurate and unambiguous indication of the position of the mobilereceiving unit at any point within the area blanketed by thetransmitting unitsv Il), and l2.

It will be observed that theunits 28, 29, 35 and 3| are connected to thereceiverV 2e and 21 only by the. cables or. conductorsV 39E and. 4| andconse-'- 17 quently the phase discriminating and position indicatingapparatus may be conveniently located, as desired, on the vehicle orvessel carrying the receiving unit I3, either closely adjacent to orremote from the receiving unit.

While a particular embodiment of the invention has been shown, it willbe understood, of course, that the invention is not limited theretosince many modifications may be made and 1t is therefore contemplated bythe appended claims to cover any such modifications as fall within thetrue spirit and scope of the invention.

What is claimed and desired to be secured by Letters Patent is:

1. Wave signal receiving apparatus for translating received spaceradiated waves into position indications, comprising wave signalreceiving means responsive to different received waves to develop twosignals having a phase relationship representative of the position ofsaid receiving apparatus relative to the sources of said waves,follow-up type indicator means including a driving motor, variable phasetransformer means energizable by one of said signals and including arotor winding driven by said motor to produce a variable phase signalhaving a phase relationship to the other of said signals which is afunc-4 tion of the phase relationship between said two signals and ofthe position of said rotor winding, and phase discriminator meansexcited by said other of said two signals and by said variable phasesignal for energizing said motor with a voltage having a magnituderelated to the phasel difference between said exciting signals andhaving a polarity indicative of the sense of the phase differencebetween said exciting signals.

2. Wave signal receiving apparatus for translating received spaceradiated waves into position indications, comprising wave signalreceiving means responsive to different received waves to develop twosignals having a phase relationship representative of the position ofsaid receiving apparatus relative to the sources of said waves,follow-up type indicator means including a driving motor, variable phasetransformer means energizable by one of said signals and including arotor winding driven by said motor to produce a variable phase signalhaving a phase relationship to the other of said signals which is afunction of the phase relationship between said two signals and of theposition of said rotor winding, and phase discriminator means excited bysaid other of said two signals and by said variable phase signal forproducing a direct current output voltage related in magnitude to thephase difference between said exciting signals and having a polarityindicative of the sense of the phase diierence therebetween, said outputvoltage being zero when said variable phase signal and said other signalhave a predetermined phase relationship therebetween, and means forenergizing said motor in accordance with said output volt- 'age to drivesaid indicating means and said rotor winding to a positionrepresentative of said predetermined phase relation.

3. Wave signal receiving apparatus for translating received spaceradiated waves into position indications, comprising wave signalreceiving means responsive to different received waves to develop twosignals having a phase relationship representative of the position ofsaid receiving apparatus relative to the sources of said waves, phaseindicator means including an indicator member, motor means for drivingsaid indicator member, variable phase transformer means having a statorand having a rotor driven by said motor means, stator and rotor windingsfor said transformer means, means for impressing one of said signals onsaid stator winding to produce in said rotor winding a variable lphasesignal having a phase relationship to the other of said signals whichisa function of the phase relationship between said two signals and of therotary position of said rotor winding, phase discriminator meansenergizable jointly by said other of said two signals and said variablephase signal for producing a direct current output voltage related inmagnitude to the phase difference between said variable phase signal andsaid other signal and having a polarity indicative of the sense of thephase difference therebetween, said output voltage being Zero when saidvariable phase signal and said other signal have a predetermined phaserelationship therebetween, and means for energizing said motor means inaccordance with said output voltage to move said indicator member and toestablish said predetermined phase relationship between said othersignal and said variable phase signal.

4. Wave signal receiving apparatus for translating received spaceradiated waves into position indications, comprising wave signalreceiving means responsive to diiferent received waves to develop twosignals having a phase relationship representative of the position ofsaid receiving apparatus relative to the sources of said waves, phaseindicator means including an indicator member, motor means for drivingsaid indicator member, variable phase transformer means having a statorand having a rotor driven by said motor means, stator and rotor windingsfor said transformer means, means for impressing one of said signals onsaid stator winding to produce in said rotor winding a variable phasesignal having a phase relationship to the other of said signals which isa function of the phase relationship between said two signals and of therotary position of said rotor winding, phase discriminator meansenergizable jointly by the other of said two signals and said variablephase signal for producing a direct current output voltage related inmagnitude to the phase difference between said variable phase signal andsaid other signal and having a polarity indicative of the sense of thephase difference therebetween, said output voltage being zero when saidvariable phase signal and said other signal have a predetermined phaserelationship therebetween, means for energizing said motor means inaccordance with said output voltage to move said indicator member and toestablish said predetermined phase relationship between said othersignal and said variable phase signal, said indicator member beingrotatable through more than 360 to indicate the phase relationshipbetween said two signals, and means for indicating the number ofcomplete revolutions made by said indicator means.

5. Wave signal receiving apparatus for translating received spaceradiated waves into position indications, comprising a first receiverfor receiving a pair of space radiated waves and for heterodyning saidwaves to produce a heterodyne signal having a frequency related to thedifference frequency between said waves, a second receiver for receivingand reproducing a reference signal having a frequency representative ofthe difference frequency between said pair of waves, null type phaseindicator means including a driving motor, variable phase transformermeans energzable by said reference signal and includingA a rotor windingdriven by said motor to produce a variable phase signal having afrequency representative of said difference frequency and having a phaserelationship Vto said heterodyne signal which is a function of the phaserelationship between said reference signal and said heterodyne signaland of the rotary position of said rotor winding, and phasediscriminator means excited jointly by said heterodyne signal and saidvariable phase signal for energizing said motor with a Ydirect currentvoltage related in magnitude to the. phase difference between saidexciting signals and having a polarity indicative of the sense of phasedifference therebetween.

6. Wave signal receiving apparatus for translating received spaceradiated waves into positiony indications, comprising a first receiverfor receiving a pair of space radiated waves and for heterodyning saidwaves to produce a heterodyne signal having a frequency related to thedifference frequency between said waves, a second receiver for receivingand reproducing a reference signal having a frequency representative ofthe difference frequency between said pair of waves, null type phaseindicator means including a driving motor, variable phase transformermeans energizable by said reference signal and including a rotor windingdriven by said motor to produce a variable phase signal having afrequency representative of said difference frequency and having a phaserelationship to said heterodyne signal which is a function of the phaserelationshipV between said reference signal and said heterodyne signaland of the rotary position of said rotor winding, phase discriminatormeans excited jointly by said heterodyne signal and said variable phasesignal for energizing said motor with a direct current voltage relatedin magnitude to the phase difference .between said exciting signals,said indicator means being rotatable by said motor through more than360, and means for indicating the number of complete revolutions madebysaid indicator means.

7. Wave signal receiving apparatus for translating received spaceradiated waves into position indications, comprising a first receiverfor receiving a pair of'space rediated waves and for heterodyning saidwaves to produce a heterodyne signal having a frequency related to thedifference frequency between said waves, a secondy receiver forreceiving and reproducing a reference signal having a frequencyrepresentative of the difference frequency between said pair ofv waves,null type phase indicator means including a driving motor, variablephase transformer means energizable'by said reference signal andincluding a rotor winding rotatably driven by said motor to produce avariable phase signal having a frequency representative of saiddifference frequency and having a phase relationship to said heterodynesignal which is a function of the phase relationship between saidreference signal and said heterodyne signal and of the rotary positionof said rotor winding, phase discriminator means energiza-ble jointly bysaid heterodyne signalr and said variable phase signal for producing adirect current output voltage related in magnitudeto the phasedifference between said variable phase signalk and said heterodynesignal and having a polarity indicative of the sense of the phasedifference therebetween, said output voltage being zero when saidvariable phase signal and said heterodyne signal have a predeterminedphase relationship therebetween, and means for energizing said 20. motor:in accordance with said :output voltager to' move said indicator memberand to move said rotor winding to a :position wherein said predeterminedphase` relationship is established between said heterodyne signal andsaid variable phase signal.

v8. Wave signal receiving apparatus for translating received spaceradiated waves into position indications, comprising a first receiverfor receiving a pair of space radiated waves and for heterodyning saidwaves to produce a heterodyne signal having a frequency related to thedifference frequency between said waves, a second receiver for receivingand reproducing a reference signal having a frequency representative ofthe difference frequency between said pair of waves, phase indicatormeans includingl an indicator member, motor means for driving saidindicator member, variable phase transformer means having a stator andhaving a rotor driven by said motor means, stator and rotor windings forsaid transformer means, means for impressing said reference signal onsaid stator winding to produce in said rotor winding a variable phasesignal having a frequency representative of said difference frequencyand having a phase relationship to said heterodyne signal which is afunction of the phasel relationship between said reference signal andsaid heterodyne signal and of the vrotary position of said rotorwinding, phase discriminator means energizable jointly by saidheterodyne signal and said 'variable phase signal for producing a directcurrent output voltage related in magnitude Vto the phase differencebetween said variablephase signal and. said heterodyne signal and havinga polarity indicative of the sense ofv the phase differencetherebetween, said output voltage being zero when said variable phasesignal and said heterodyne signal have a predetermined phaserelationship therebetween, and means for energizing said motor means inaccordance with said output voltage to move said indicator member and toestablish said predetermined phase relationship between said heterodynesignal and said Variable phase signal.

9. Wave signalv receiving apparatus for translating receivedg; spaceradiated waves into position indications, comprising a receiveroperating to receive a first pair of space radiated waves and toheterodyne said waves to produce a first heterodyne signal having afrequency related to thel difference frequency between said waves, saidreceiver b eing alternately operative to receive and reproduce arst,reference signal having a frequency representative of the dierence fre,-quency. .between a second pair of radiated waves and modulated upon oneof said first pair of` radiated waves, a second receiver operative toreceive and heterodyne said second pair of radiated waves to produce asecondheterodyne signal having a frequency equaling the frequency ofsaid rst reference signal, said second receiver being alternatelyoperative toreceive and reproduce a second reference signalhaving afrequency representative of the difference frequency between said firstpair of waves and modulated upon one of said second pair of waves, phasemeasuring. and indicating. means excited by said signalsin-pairs-andincluding a pair of indicators rotatable through more than360 to indicate the phase relationship between said rst heterodyne andsecond reference signals and between said second heterodyne and rstreference signals to provide two indications of the position of saidatenei;

receiving apparatus relative to ,two displaced sources of said waves,and means for indicating the number of complete revolutions made by eachor said indicators.

10. Wave signal receiving apparatus for translating received spaceradiated waves into position indications, comprising a receiveroperating to receive a rst pair of space radiated waves `and toheterodyne said waves to produce a rst heterodyne signal having afrequency related to the difference frequency between said waves, saidreceiver being alternately operative to receive and reproduce a rstreference signal having a frequency representative of the diierenoefrequency between a second pair of radiated waves I and modulated uponone of said first pair of radiated Waves, a second receiver operative toreceive and heterodyne said second pair of radiated waves to produce asecond heterodyne signal having a frequency equaling the frequency ofsaid iirst reference signal, said second receiver being alternately.operative to receive and reproduce a second refrence signal having afrequency representative of the difference frequency between said rstpair of waves and modulated upon one of said second pair of waves, phasemeasuring and indicating means excited by said signals in pairs andincluding a pair of indicators rotatable through more than 360 toindicate the phase relationship between said i'lrst heterodyne andsecond reference signals and between said second heterodyne and rstreference signals to provide two indications of the position of saidreceiving apparatus relative to two displaced sources of said waves,counter means for indicating the number of complete revolutions made byeach of said indicators, and means for adjusting said indicators andsaid counter means to settings corresponding to a known startingposition of said apparatus relative to said sources.

11. Wave signal receiving apparatus for translating received spaceradiated waves into position indications, comprising wave signalreceiving means responsive to different received waves to develop twosignals having a phase relationship representative of the position ofsaid receiving apparatus relative to the sources oi said waves, nulltype indicator means including an indicating element and a motor fordriving said element, variable phase transformer means including astator winding energizable by one of said signals, a rotor winding forproducing a variable phase signal, adjustable means coupling said motorto said rotor winding for variably driving said rotor winding to eifecta shift of one electrical degree in the phase of said variable phasesignal for each degree of rotation of said indicating element and phasediscriminator means excited by the other of said two signals and by saidvariable phase signal for energizing said motor with a voltage having amagnitude related to the phase difference between said eX- citingsignals and having a polarity indicative of the sense of the phasedifference therebetween.

12. Wave signal receiving apparatus for trans lating received spaceradiated waves into position indications, comprising wave signalreceiving means responsive to diirerent received waves to develop twosignals having a phase relationship representative of the dierencebetween the distances of said receiving apparatus from the sources ofsaid Waves, null type indicator means including an indicating elementand afmotor for driving said element, variable phase transformer meansincluding a stator winding energizable by one of said signals, a rotorwinding for producing a variable phase signal, adjustable means couplingsaid motor to said rotor winding for variably driving said rotor windingto effect a shift of one electrical degree in the phase of said variablephase signal for each degree of rotation of said indicating element, andphase discriminator means excited by the other of said two signals andby said variable phase signal for producing a direct current outputvoltage related in magnitude to the phase diiference between saidexciting signals and having a polarity indicative-of the sense of thephase displacement therebetween, said output voltage being zero whensaid variable phase signal and said other signal have a predeterminedphase relationship therebetween, and means for energizing said motor inaccordance with said output voltage to drive said indicating element andsaid rotor winding to a position Whereinsaid predetermined phaserelationship is established between said variable phase signal and saidother signal.

13. Wave signal receiving apparatus for ,translating received spaceradiated waves into position indications, comprising a rst receiver forreceiving a pair of space radiated waves and for heterodyning said wavesto produce a heterodyne signal having a frequency related to thedifference frequency between said waves, a second receiver for receivingand reproducing a reference signal having a frequency representative ofthe difference frequency between said pair of waves, null type phaseindicator means including an indicating element and a motor for drivingsaid element, variable phase transformer means including a statorwinding energizable by said reference signal, a rotor winding movablewith respect to said stator winding for producing a variable phasesignal, adjustable means coupling said motor means to said rotor windingfor variably driving said rotor Winding to produce a shift of oneelectrical degree in said variable phase signal for each degree ofrotation of said indicating element, phase discriminator meansenergizable jointly by said heterodyne signal and said variable phasesignal for producing a direct current output voltage related inmagnitude to the phase difference between said variable phase signal andsaid heterodyne signal and having a polarity indicative of the sense ofthe phase difference therebetween, said output voltage being zero whensaid variable phase signal and said heterodyne signal have apredetermined phase relationship therebetween, and means for energizingsaid motor in accordance with said output voltage to move said indicatormember and to adjust said rotor winding to a position wherein saidpredetermined phase relationship is established between said heterodynesignal and said variable phase signal.

14. Apparatus for indicating the phase relationship between two signalsof the same frequency which may have a phase relationship variablebetween zero and three hundred and sixty electrical degrees, comprisingindicator means and a motor for driving said indicator means, variablephase transformer means having a rotor driven by said motor, stator androtor windings for said transformer means, means for impressing one ofsaid signals on said stator winding to induce in said rotor winding avariable phase signal having the same frequency as 23 'said one signaland having a .phase relationship to said one (signal which -is a-function of the rotary position of said rotor winding .relative rtosaid stator winding, phase discriminator means energizable jointly bythe other of said signals and said variable phase signal lfor producinga direct current output voltage related in magnitude to the phasedifference between said Variable phase signal and said other signal andhaving a 'polarity indicative of the sense of the phase dierencetherebetween, said output Voltage being zero when said variable phasesignal and said other signal have a predetermined 'phase relationshiptherebetween, and means for eil-7 ergizing said motor in accordance withsaid output voltage to drive said indicator means and simultaneously torotate said rotor winding relative to said stator wind-ing to establishsaid predetermined phase relationship between said variable phase signaland said other signal.

15. Apparatus for indicating the phase relationship between t-wosignalsof the same frequency which may have a phase relationshipvariable between zero and three hundred and sixty electrical degrees,comprising indicator means and a motor for driving said indicator means,variable phase transformer means including a stator and a rotor, statorand rotor windings for said transformer means, means for impressing oneof said signals on said stator winding to induce in said rotor winding avariable phase signal having the same frequency as said one signal andhaving a phase relationship tosaid one signal which is a function of theyangular position of said rotor winding relative 4to said statorwinding, adjustable means cou-'- pling said motor means to said rotorfor Variably rotating said rotor `winding to produce a shift 'of oneelectrical degree in said variable .phase signal @for each degree ofmovement of said in#- dicator means, phase discriminator meansenergiz'able jointly b'y 'the other of said signals and said variablevphase signal for producing a direct current' output voltage related inmagnitude to the phase `difference between said variable phase signaland said other signal and have ingzapolarity indicative of the sense ofthe phase differenceV therebetween, said output voltage being' 'zero'when said variable phase signal and saidl other signal have Vapredetermined phase relationslfiipv therebetween, and means forenergizing said motor' in accordance withsaid out;- put voltage to drivesaid indicator means and simultaneously to rotate said rotor Windingrelative to said 'stator winding to 'establish said pre= determinedphase relationship between said var iable phase signal and said othersignal.

JAMES E. HAWKINS. BEVERLY W. KOEPPEL.

REFERENCES CITED The' following references are of record in the file ofthis patent:`

UNITED STATES PATENTS

